This application claims priority to European Application No. 00202797.7 filed on Aug. 7, 2000.
The invention relates to a method of measuring a down-web coordinate on a web by relating a time-interval, elapsed since a detection of a position-indicating mark applied on said web, to a measured velocity. The invention also relates to a system for carrying out the method and for tracking the position of quality problem areas at continuous-web products. The invention also relates to photographic paper for use in such a system.
Photographic paper is produced as a continuous web, starting with a roll of base paper to which at both sides a sheet containing at least water repellent poly-olefin resin is extrusion coated. In the next manufacturing step a number of photographic emulsions are coated on the top side of said web.
During production of the base paper and the extrusion-coating of the poly-olefin resin layers onto said base paper as well as during the coating of the photographic emulsions, areas with quality problem may occur. These quality problem areas are usually detected by a laser beam analyzer that inspects the full width of the web and exactly registers the cross web coordinate. Additionally the metric down web coordinate is registered at which the quality problem area on the web passes the detector. The term xe2x80x9cdown-webxe2x80x9d is referring to an orientation in the winding direction of a web that is winded on a roll; the term xe2x80x9ccross-webxe2x80x9d is referring to an orientation in the plane of the web and perpendicular to the xe2x80x9cdown-webxe2x80x9d direction.
The down web coordinate of the quality problem area is not exactly measurable but provides a reasonable indication. The down web coordinate is related to the splice at the beginning of the roll and the speed of the web in relation to the time that has passed since said splice passed the laser beam analyzer. Due to physical phenomena, like slip and stretch, the measured web-length deviates from the actual transported length. This may cause deviation in the measurement of the length coordinate.
The large roll is slitted in the length direction at a special machine into various small rolls, called baby-rolls, that are used in the developing/processing machines at the photo laboratories. In order to be sure that a quality problem area is eliminated from a small roll, a considerable length, say more than 10 meters before and after the indicated down web coordinate, is discarded from that roll. The roll is rewinded and a considerable length of the photographic web is replaced by a part without any quality problem areas. This results in two splices to connect an inserted part. These splices are identified by so called splice indicating holes, as has been stipulated in an ISO-standard, further called ISO-holes, see EP-A-490 398. The ISO-holes are detectable by the image printing machines of the photo laboratories. These small splicing parts of the roll are discarded.
An object of the invention is to register precisely a down-web coordinate on a web-product. A further object of the invention is to register precisely the down web coordinate of a quality problem area as located in or at the photographic products or at the front or back of continuous web products. Yet another object of the invention is to discard as little material as possible, at removal of the quality problem area from the web.
Still object of the invention is the application of digital product markings at the back of the continuous web, comprising product information like: the roll orientation, the product type code, the product lot number, the roll number, etc.
Another object of the invention is to mark the quality problem area by punching an ISO-hole very close to the quality problem area.
Another object of the invention is the reduction of product losses due to quality problems.
Another object of the invention is the reduction of web handling operations necessary for discarding the web parts with quality problems.
The above mentioned objects are obtained by using the method of the preamble, wherein, upon detection of a position-indicating mark, the measured down-web coordinate is synchronised with the indicated down-web coordinate of said mark.